1. Technical Field
The present invention relates to impedance correction, and more particularly to an impedance correction device and a method thereof.
2. Related Art
Currently, an impedance of a high-speed transmission interface on the market is usually defined with a certain value, so that designers can pre-design the output capability of a similar impedance value, thereby matching impedances, reducing reflected waves, and reducing noise. However, most designs of the transmission interface on the market only take into consideration such factors as process shift, difference of external voltage, and change of environmental temperature, without considering the possible influence caused by a circuit board itself.
FIG. 1 is a conventional technology of impedance correction. Within a circuit, a precision resistor Rref is generally designed outside an integrated circuit, and is connected to ground VSSQ. An internal resistor R is connected to a power supply VDDQ. The voltage at a point 6 can be obtained through the principle of voltage division. The voltage at the point 6 is the same as the voltage at a point 5. Comparing with the voltage at a point 4 of a working circuit 1, if the voltage at the point 5 is smaller than a comparison voltage Vcomp at the point 4, a comparator 3 will output the voltage difference to a control circuit 2, which will output a control signal to reduce the resistance of the internal resistor R. On the contrary, if the voltage at the point 5 is greater than the comparison voltage Vcomp at the point 4, the control circuit outputs another control signal to increase the resistance of the internal resistor R. Thus, impedance matching can be achieved by adjusting the impedance value of the internal resistor R.
The conventional technology requires the installation of a precision resistor outside the integrated circuit, which is costly and cannot appropriately handle the possible influence caused by the impedance value of paths on the circuit board.